Python – Canonical Way to Check for Type

pythontypes

How do I check if an object is of a given type, or if it inherits from a given type?

How do I check if the object o is of type str?

Beginners often wrongly expect the string to already be "a number" – either expecting Python 3.x input to convert type, or expecting that a string like '1' is also simultaneously an integer. This is the wrong canonical for those questions. Please carefully read the question and then use How do I check if a string represents a number (float or int)?, How can I read inputs as numbers? and/or Asking the user for input until they give a valid response as appropriate.

Best Answer

Use isinstance to check if o is an instance of str or any subclass of str:

if isinstance(o, str):

To check if the type of o is exactly str, excluding subclasses of str:

if type(o) is str:

See Built-in Functions in the Python Library Reference for relevant information.

Checking for strings in Python 2

For Python 2, this is a better way to check if o is a string:

if isinstance(o, basestring):

because this will also catch Unicode strings. unicode is not a subclass of str; both str and unicode are subclasses of basestring. In Python 3, basestring no longer exists since there's a strict separation of strings (str) and binary data (bytes).

Alternatively, isinstance accepts a tuple of classes. This will return True if o is an instance of any subclass of any of (str, unicode):

if isinstance(o, (str, unicode)):
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